This application claims benefit of priority under 35USC xc2xa7119 to Japanese patent application No. 2000-089909, filed on Mar. 28, 2000, the contents of which are incorporated by reference herein.
1. Field of the Invention
The present invention relates generally to a charged particle beam system. More specifically, the invention relates to observation, inspection and measurement using charged particle beams.
2. Description of the Prior Art
A typical process for producing a semiconductor device includes a step of measuring the dimension of a pattern which is formed on a substrate such as a wafer or a reticle. In the measurement of the dimension of such a pattern, a critical dimension measurement SEM (Scanning Electron Microscope) having a length measuring function is usually used for acquiring a top-down image of the pattern to measure pattern widths, hole diameters and so forth in the top-down image.
In recent years, three-dimensional information such as the shape of the sidewall of a pattern, not only such two-dimensional information, is being an important evaluated item in an actual producing process. Conventionally, a cross-section SEM, a review SEM or the like is used for obtaining the three-dimensional information of a pattern.
However, the cross-section SEM takes a lot of time to carry out processing, since a sample must be broken into minute pieces and be mounted on a predetermined jig. In addition, the cross-section SEM is not suitable for an in-line evaluation for carrying out an evaluation in a producing process, since it is a destructive inspection.
On the other hand, the review SEM is a system for causing electron beams to be obliquely incident on a sample to observe the three-dimensional shape of a pattern by slanting a sample table of a scanning electron microscope together with a transporting mechanism. The review SEM is more suitable for an in-line evaluation than the cross-section SEM, since it is not required to process the sample.
However, the motion of the review SEM is slow since the sample table and a stage are mechanically slanted. In addition, since the review SEM is a separate system from the above-described critical dimension measurement SEM, there is the possibility that the number of producing steps may increase. In order to solve this problem, it is considered that a tilted stage is mounted on the critical dimension measurement SEM. However, it is required to provide a complicated stage mechanism in order to slant a sample table, so that there are problems in that the size of the system increases and the positioning accuracy of the stage deteriorates. For that reason, it is difficult to mount the tilted stage on the critical dimension measurement SEM in the present circumstances.
It is therefore an object of the present invention to eliminate the aforementioned problems and to provide a charged particle beam system and a pattern slant observing method, which can be used for carrying out an in-line evaluation and which have a rapid, high-accuracy slant observing function.
According to the first aspect of the invention, there is provided a charged particle beam system comprising:
a charged particle beam emitting device for generating charged particle beam and for irradiating a sample to be inspected with the charged particle beam; a condenser lens for condensing the charged particle beam; a scanning deflecting device for deflecting the charged particle beam to scan the charged particle beam on the sample; an objective lens for focusing the charged particle beam on the surface of the sample; a slant observing deflecting device, arranged between the objective lens and the sample, for deflecting the charged particle beam to cause the charged particle beam to be obliquely incident on the sample at an optional slant angle from a beam axis of the charged particle beam; a charged particle detector for detecting a secondary charged particle and/or a reflected charged particle which are generated from the sample irradiated with the charged particle beam; and a control part for controlling the slant angle.
According to the present invention, a slant observing deflecting device provided between the objective lens and the sample slants deflects charged particle beams immediately before the charged particle beams are incident on the sample, so that it is possible to acquire a slant image of the surface of the sample while preventing a deterioration of an electron-optics property due to the bending of the trajectory of the beams.
The control part may preferably include an irradiation position shift correcting part for correcting an irradiation position shift caused by the charged particle beam which is obliquely incident on the sample.
By the irradiation position shift correcting part, it is possible to easily correct the observation position of the slant image, so that it is possible to rapidly observe the slant.
It is preferable that the irradiation position shift correcting part has: an irradiation position shift quantity calculating part for calculating a magnitude and a direction of the irradiation position shift on the basis of the slant angle; and a scanning deflection control part for controlling the scanning deflecting device on the basis of the calculated result of the irradiation position shift quantity calculating part to shift the trajectory of the charged particle beam by a distance according to the magnitude of the irradiation position shift in the opposite direction to the direction of the irradiation position shift.
According to the second aspect of the invention, there is provided a charged particle beam system comprising:
a charged particle beam emitting device for generating a charged particle beam and for irradiating a sample to be inspected with the charged particle beam; a condenser lens for condensing the charged particle beam; an objective lens for focusing the charged particle beam on the surface of the sample; a scanning/slant observing deflecting device, arranged between the objective lens and the sample, for deflecting and scanning the charged particle beam and for causing the charged particle beam to be obliquely incident on the sample at an optional slant angle from a beam axis of the charged particle beam; a charged particle detector for detecting a secondary charged particle and/or a reflected charged particle which are generated from the sample irradiated with the charged particle beam; and a control part for controlling the slant angle.
According to the charged particle beam system, it is possible to simultaneously control the scanning deflection and slant observing deflection of electron beams since it has the scanning/slant observing deflecting device.
The charged particle beam system of the second aspect of the invention may advantageously further comprises: an irradiation position shift quantity calculating part for calculating a magnitude and a direction of an irradiation position shift, which occurs when the charged particle beam is obliquely incident on the sample, on the basis of the slant angle; and an irradiation position shift correcting part for controlling the scanning/slant observing deflecting device to correct the irradiation position shift on the basis of the calculated result of the irradiation position shift quantity calculating part.
The charged particle beam system of the second aspect of the invention may preferably further comprise a correction deflecting device, arranged between the condenser lens and the objective lens, for shifting the trajectory of the charged particle beam by a distance according to the magnitude of the position shift in the opposite direction to the direction of the position shift on the basis of the calculated results of the irradiation position shift quantity calculating part to correct the irradiation position shift, the correction deflecting device constituting an irradiation position shift correcting part.
The above mentioned charged particle beam system may further comprise a stage for supporting the sample, the stage being movable on a plane substantially perpendicular to the beam axis of the charged particle beams, and the irradiation position shift correcting part may include a stage control part for moving the stage by a distance according to the magnitude of the irradiation position shift in the direction of the irradiation position shift calculated by the irradiation position shift quantity calculating part, in place of the control of the scanning deflecting device or the scanning/slant observing deflecting device.
The charged particle beam system may further comprise an image processing part for converting the secondary charged particle and/or the reflected charged particle into image data, and a display for displaying the image data as a charged particle beam image, the secondary charged particle and/or the reflected charged particle being detected by the charged particle detector, and the irradiation position shift correcting part has an irradiation position shift quantity calculating part for calculating a magnitude and a direction of the irradiation position shift on the basis of the slant angle, and an image correcting part for controlling the image processing part so that the charged particle beam image is displayed at a desired position on the display on the basis of the calculated results, in place of the control of the scanning deflecting device, the scanning/slant observing deflecting device or the stage.
In addition, in place of the above mentioned control of the scanning deflecting device, the scanning/slant observing deflecting device, the stage or the image processing part, the irradiation position shift correcting part may further have an objective lens correction control part for controlling the objective lens on the basis of the calculated result of the irradiation position shift quantity calculating part to move the objective lens so that the trajectory of the charged particle beam shifted by the scanning deflecting control part passes through the center of the objective lens.
It is preferable that the objective lens correction control part electromagnetically moves the objective lens by shifting an electromagnetic field which is generated by the objective lens. Alternatively, the charged particle beam system may further comprise a movable lens supporting body for supporting the objective lens, and the objective lens correction control part may mechanically move the objective lens by moving the lens supporting body.
The control part of the charged particle beam system may preferably control the slant observing deflecting device or the scanning/slant observing deflecting device so that an ununiform electric field is generated at a position, at which the charged particle beam is emitted from the slant observing deflecting device or the scanning/slant observing deflecting device, or in a region in the vicinity of the point. Thus, the slant observing deflecting device or the scanning/slant observing deflecting device deflects the charged particle beams immediately before the charged particle beams are incident on the sample, to deflect the trajectory of the charged particle beams at the slant angle, so that it is possible to rapidly acquire the slant image of the surface of the sample while preventing the deterioration of the electron-optics property. Thus, it is possible to inspect the shape of the surface of the sample in-line. The ununiform electric or magnetic field can be formed by applying a DC voltage component to an electrode or coil, which is positioned in a direction for slanting the charged particle beams, of the electrodes or coils of the slant observing deflecting device or the scanning/slant observing deflecting device, and by applying no DC voltage component to the electrode or coil, which is positioned at the opposite direction, when the slant observing deflecting device or the scanning/slant observing deflecting device has the electrode or coil in the opposite direction to the direction in which the slant is intended.
The slant observing deflecting device or the scanning/slant observing deflecting device is preferably an electrostatic deflecting device. Thus, it can be more inexpensively prepared than a stage slant mechanism, so that it is possible to rapidly and easily carry out a slant observation with excellent linearity by retrofitting the existing systems.
The electrostatic deflecting device may advantageously include an insulator which is provided between the objective lens and the sample and on which a metal film is deposited, and the metal film constitutes an electrode of the electrostatic deflecting device.
Furthermore, the charged particle beam system may preferably further comprise a shielding electrode, incorporated in the electrostatic deflecting device, for shielding the objective lens from the electric field which is generated by the electrostatic deflecting device.
By the shielding electrode, an electric field shielding is formed between the bottom face of the objective lens and a region immediately before the charged particle beams are incident on the surface of the sample. Thus, it is possible to prevent a deterioration of an electron-optics property, such as lens aberration, of the charged particle beams.
According to the third aspect of the invention, there is provided a pattern slant observing method using a charged particle beam system which comprises a charged beam source, a charged particle beam optical system, a stage for supporting a sample on which a pattern is formed, and a charged particle detector, the electron-optical system including a scanning deflecting device and an objective lens, the pattern slant observing method comprising: an irradiation step of emitting a charged particle beam from the electron gun and of irradiating the sample with the charged particle beam; a scanning step of deflecting the charged particle beam by the scanning deflecting device to scan the charged particle beam on the sample; a focusing step of focusing the charged particle beam on the surface of the sample by the objective lens; a slant incident step of forming an ununiform electric field or an ununiform magnetic field at a position at which the charged particle beam is emitted from the electron-optical system or in a region in the vicinity of the position, of deflecting the charged particle beam by the electric or magnetic field so that the focused charged particle beam has an optional slant angle from a beam axis of the charged particle beam and of causing the charged particle beam to be obliquely incident on the sample; a detection step of detecting a secondary charged particle and/or a reflected charged particle which are generated from the sample by irradiation with the charged particle beam; and an image data acquiring step of acquiring image data, which are to be a slant image of the pattern, on the basis of the secondary charged particle and/or the reflected charged particle.
By the slant incident step, the charged particle beams are deflected by the ununiform electric or magnetic field, so that the charged particle beams are deflected intermediately before being incident on the sample, to be obliquely incident on the sample at the slant angle. Thus, it is possible to acquire the slant image of the pattern, which is formed on the surface of the sample, while preventing a deterioration of an electron-optics property.
The pattern slant observing method may advantageously further comprise an electromagnetic shielding step of preventing the electric or magnetic field from entering the trajectory of the charged particle beam on the side of the electron gun from a region in which the charged particle beam is deflected at the slant angle from the beam axis.
The pattern slant observing method may also advantageously further comprise an irradiation position shift quantity calculating step of calculating a magnitude and a direction of an irradiation position shift, which occurs when the charged particle beam is obliquely incident on the sample, on the basis of the slant angle, and the scanning step may include a step of shifting the trajectory of the charged particle beam by a distance according to the magnitude of the irradiation position shift in the opposite direction to the direction of the irradiation position shift on the basis of the calculated results at the irradiation position shift quantity calculating step. By the step of shifting the beam trajectory, the irradiation position shift of the charged particle beams is corrected, so that it is possible to rapidly observe the slant.
The pattern slant observing method may preferably further comprise a step of moving the objective lens on a plane substantially perpendicular to the beam axis of the charged particle beam in accordance with the shift of the trajectory of the charged particle beam so that the shifted charged particle beam passes through the center of the objective lens.
When the stage of the charged particle beam system is movable on a plane which is substantially perpendicular to the beam axis of the charged particle beams, the pattern slant observing method preferably further comprises a step of moving the stage in the direction of the irradiation position shift by a distance according to the irradiation position shift quantity on the basis of the calculated results at the irradiation position shift quantity calculating step, in place of the control of the scanning deflecting device or the scanning/slant observing deflecting device.
In addition, when the charged particle beam system further comprises a display for displaying the image data as a charged particle beam image, the pattern slant observing method may further comprise; an irradiation position shift quantity calculating step of calculating a magnitude and a direction of an irradiation position shift, which occurs when the charged particle beam is obliquely incident on the sample, on the basis of the slant angle; and an image correcting step of correcting the image data so that the charged particle beam image is displayed at a desired position on the display on the basis of the calculated results instead of the control of the scanning deflecting device, the scanning/slant observing deflecting device or the stage.
The scanning step of the pattern slant observing method may preferably be carried out simultaneously with the slant incident step at a position, at which the charged particle beam is emitted from the electron-optical system, or in a region in the vicinity of the position.
Furthermore, the pattern slant observing method may further comprise a correction deflecting step of shifting the trajectory of the charged particle beam by a distance according to the magnitude of the irradiation position shift in the opposite direction to the direction of the irradiation position shift, at the point at which the charged particle beam is emitted from the electron-optical system, or in a region in the vicinity of the point, or in a region which is more closer to the electron gun than the objective lens in the electron-optical system, on the basis of the calculated results at the irradiation position shift quantity calculating step instead of the control of the scanning deflecting device, the scanning/slant observing deflecting device, the stage or the image processing part.